Hydrocarbon exploration involves drilling deep within the earth to find hydrocarbon-producing formations. To drill a wellbore, a drill bit is provided at the end of a drill string and rotated to form a wellbore. One type of a drill bit is the fixed-cutter drill bit. Such drill bits generally include an array of cutters secured to a face region of the bit body. The cutters of a fixed-cutter drill bit generally have a substantially cylindrical shape. A hard, superabrasive material, such as polycrystalline diamond, may be provided on each cutter, providing a cutting surface for engaging the formation during drilling. Such cutters are often referred to as polycrystalline diamond compact (PDC) cutters. Typically, the cutters are fabricated separately from the bit body and secured within cutter recesses or pockets formed in the outer surface of the bit body. A bonding material, such as a braze alloy, may be used to secure the cutters to the bit body. A fixed-cutter drill bit is placed in a borehole such that the cutters are in contact with the earth formation to be drilled. As the drill bit is rotated, the cutting elements scrape across and shear away the surface of the underlying formation.
The body of the drill bit may be formed from a metal-matrix composite material. Such materials include reinforcement particles randomly dispersed throughout a matrix material, often referred to as a binding material. Metal-matrix composite bit bodies may be formed by embedding a metal mandrel or blank in a particulate material volume, such as particles of tungsten carbide, and then infiltrating the particulate material with a matrix material, such as a copper alloy.
Drill bits that have a body formed from such metal-matrix composites offer significant advantages over all-steel bit bodies, including increased erosion and wear resistance, but generally have lower toughness and other constraints, such as lower blade standoff, that limit their use in certain applications. In particularly harsh drilling environments involving complex loading of the drill bit, metal-matrix composite bodies subject to extremes of cyclical loading are known to be subject to various forms of cracking. Once a crack is initiated, further cyclical loading can cause the crack to propagate through the matrix and can lead to premature failure of the bit. Such failures are costly, as they generally require cessation of drilling while the drill string and drill bit are removed from the borehole for repair or replacement of the drill bit.